Do hydrodynamic factors affect the recruitment of marine invertebrates in a macrotidal area?

Abstract

For marine benthic invertebrates exhibiting complex life cycles, changes in populations’ distribution and abundance are governed by a large variety of physical, chemical and biological processes. From field observations in the Bay of Seine and laboratory experiments conducted since 1987 on the polychaete Pectinaria koreni, the present study highlights the relative importance of hydrodynamical and biological factors which affect individuals within both the planktonic and benthic phases at different scales of space and time in a macrotidal area. Pectinaria koreni is one of the main macrofaunal component of the Abra alba muddy fine sand community of the eastern Bay of Seine. Despite a highly advective and diffusive environment, a relative larval retention near adult population was reported due to some local hydrodynamics features (e.g. tidal residual circulation, Seine river plume front) and the interaction between the vertical current structure and the larval vertical migration. Although larval retention could be disrupted by wind induced currents, multiple spawning events over the reproductive period increase the likelihood that at least one larval cohort ensures a high recruitment during the life-span. Following a massive settlement whatever the sediment grain size, the newly settled larvae exhibited a high immediate decrease of their densities as a result of postlarval mortality and migration. Postlarval drifting was induced by a combination of physical factors (i.e. tidal currents and swell) and postlarval behaviour in response to sediment texture and adult/settlers interactions. According to the hydrodynamics of the bay, this process may generate a postlarval transport from offshore bottoms to coastal suitable habitats and counteract the demographic effects of larval dispersal. A conceptual model of factors governing the recruitment and population maintenance of Pectinaria koreni is proposed and discussed in comparison with results obtained on another polychaete, Owenia fusiformis, in the same area.